Radio communication system and base station employing CDMA

ABSTRACT

A base station controller selects codes corresponding to rate information included in a new starting call message from a mobile station, and further selects codes assignable to the mobile station out of the selected codes as candidate codes. Then, the base station controller detects codes which meet both the characteristics of being at upper level of the candidate codes in the tree structure and being assignable to other mobile station, and further detects levels of the detected codes. Detected levels for all the candidate codes are compared to find a candidate code whose level is the lowest and to assign the candidate code to the mobile station sending the new starting call message.

This application is a divisional of U.S. patent application Ser. No.10/013,451 filed on Dec. 13, 2001, which is a continuation of U.S.patent application Ser. No. 09/156,703 filed on Sep. 18, 1998 (now U.S.Pat. No. 6,477,158), all of which claim priority to JP 10-065434filed onMar. 16, 1998, the contents of each of which being hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to code assignment in multi-ratecommunications of the radio communication system employing Code DivisionMultiple Access (CDMA) system, where codes having tree structuredorthogonal multi-spreading factor sequence are used as spreading codes.

2. Description of the Related Art

The system utilizing coherent multi code and the system utilizing treestructured multi-spreading factor sequence code have been introduced asa multi-rate transmission system in the radio communication systememploying DS-CDMA (Direct Sequence-CDMA). In the multi-rate transmissionutilizing the coherent multi code, plural codes are simultaneously usedto perform multi-code-multiplexing. In the multi-rate transmissionutilizing the tree structured multi-spreading factor sequence code,orthogonal codes having equivalent spreading factors are multiplexed inparallel. Receivers for receiving plural codes are needed for a mobilestation used for the multi-rate transmission utilizing the coherentmulti code. On the other hand, only one receiver is needed for thesystem utilizing the tree structured multi-spreading factor sequencecode.

The conventional CDMA system using tree structured orthogonalmulti-spreading factor sequences is disclosed in, for example, atechnical report entitled “Multi-rate Wideband DS-CDMA Radio Access ForNext Generation Mobile Radio Systems”, the Institute of Electronics,Information and Communication Engineers, RCS-97-86, 1997. Theconventional system will be explained with reference to FIG. 11.

FIG. 11 shows a configuration of the conventional tree structuredorthogonal multi-spreading factor sequences.

The tree structure is composed of four levels: level 1 at the topthrough level 4 at the bottom, defined just for convenience. As thereare four levels in this case, the channel transmission rate using thetop level (level 1) code is eight times as fast as that of the channelusing the lowest level (level 4) code. The channel transmission rateusing level 2 code is four times the rate of channel using the level 4code. The channel transmission rate using level 3 code is twice the rateof channel using the level 4 code. Cx(y) in FIG. 11 represents a kind ofcodes, x stands for a code level, y stands for an identification numberin the same code level, and ◯ stands for a code.

In FIG. 11, a code in the level 1 can be used for communication of twicethe transmission rate of level 2. Now, a concrete example will beexplained referring to the case of tree structure as shown in FIG. 11.When C₂(1) is assigned to a user of four times the transmission rate ofthe lowest rate (C₄(x) level in FIG. 11), the codes C₄(1), C₄(2), C₄(3),C₄(4), C₃(1), and C₃(2) can not be assigned to other users because ofkeeping the code orthogonality. Due to this characteristic, all thelower level codes connected with an assigned code through branches andall the upper level codes connected with the assigned code through onlyupward branches are not-assignable. When C₂(1) is the assigned code, allthe lower codes C₄(1), C₄(2), C₄(3), C₄(4), C₃(1) and C₃(2) connectedwith the assigned code by branches are not-assignable, and the uppercode C₁(1) connected with the assigned code by the shortest branch isnot-assignable, either.

As stated above, in CDMA system using codes of tree structuredorthogonal multi-spreading factor sequences, the code assignment for amobile station is restricted because of the characteristic. Accordingly,in the case of FIG. 11, if C₄(5) and C₄(7) are assigned to calls of thelowest rate (level 4), it is impossible to assign a call having the rateof level 3 or upper than level 3. However, on the supposition that C₄(6)is assigned to the call of level 4 instead of C₄(7), it is possible toassign C₃(4) to the call of level 3, consequently channels areeffectively utilized.

OBJECTS OF THE PRESENT INVENTION

In the multi-rate transmission of the conventional radio communicationsystem employing Code Division Multiple Access (CDMA) system where codeshaving tree structured orthogonal multi-spreading factor sequence areused, when a code has been already assigned (in use), it is impossibleto assign all the codes upper than the code. This causes a problem thatthe channel utilization is deteriorated. It is an object of the presentinvention to utilize all the system (all the branches) of the treestructure for assigning a code to be responsive to a new call, in orderto enhance the channel utilization.

In the conventional art, a channel mismatch would occur at the callending, even if a channel match was kept at the code assigning time of anew call starting. This sometimes causes a problem that selecting a codeto be assigned to a new call is impossible. It is another object of thepresent invention is to avoid the channel mismatch by switching a codebeing used in communication. Consequently, call loss rate can bereduced.

In the code assignment of the conventional radio communication systememploying CDMA system, it is necessary for a base station and a mobilestation to simultaneously switch codes in order not to stop thecommunication under way. However, as the base station does not havemeans for judging a code switch timing over the mobile station, the basestation is troublesomely needed to simultaneously perform reception andtransmission using both the codes used before and after switching. It isanother object of the present invention to reduce the stop time causedby code switching and the hardware needed for reception/transmissionusing both the codes between the base station and the mobile station, bymeans of sending the code switching timing from the base station.

In the code assignment of the conventional radio communication systememploying CDMA system, there is a problem that much process is neededfor synchronizing the code switch timings in the base station and themobile station. It is another object of the present invention to reducethe code switching process by means of depending on mobile station's owntiming.

Namely, it is a general object of the present invention to provide anapparatus and a method for effectively utilizing the channel, comprisingmeans in the base station to judge a code switch timing over the mobilestation, and reducing the synchronization process.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a code assigningapparatus used in a radio communication system including a base stationcontrolling apparatus, a plurality of base stations, and a plurality ofmobile stations, employing CDMA (Code Division Multiple Access) method,which uses codes of tree structured orthogonal multi-spreading factorsequences as spreading codes, for radio access between the plurality ofbase stations and the plurality of mobile stations, and providingmulti-rate transmission between the plurality of mobile stations and theplurality of base stations, the code assigning apparatus comprises

a code selecting unit for selecting an assignable code which suitsspecifications requested by a new starting call and exists in a locationas close to a not-assignable code as possible and in a level lower thanthe not-assignable code in the tree structure.

According to another aspect of the present invention, the code selectingunit of the code assigning apparatus comprises

a first selecting unit for selecting one or more than one codescorresponding to rate information included in a message from one of theplurality of mobile stations, as first codes,

a second selecting unit for selecting one or more than one first codesif they are assignable to the one of the plurality of mobile stations,as second codes,

a level detecting unit for retrieving codes upper than the second codesone by one, detecting not-assignable codes, which are assigned toanother of the plurality of mobile stations, out of the codes upper thanthe second codes, as third codes, and detecting each level of the thirdcodes,

a third selecting unit for selecting one of the second codes whose upperthird code is in a lowest level in the tree structure, and

a code assigning unit for assigning the one of the second codes selectedby the third selecting unit to the one of the plurality of mobilestations.

According to another aspect of the present invention, the code assigningapparatus comprises

a code-switching/code-assignment processing unit, when there is noassignable code which suits specifications requested by a new startingcall, for making a code which is not-assignable and suits thespecifications requested by the new starting call assignable by way ofswitching an assigned code being used to another code connected by abranch different from a branch used for the assigned code in the treestructure.

According to another aspect of the present invention, thecode-switching/code-assignment processing unit of the code assigningapparatus comprises

a first selecting unit for selecting one or more than one codescorresponding to rate information included in a message from the secondmobile station, as first codes,

a second selecting unit for selecting one or more than one first codesif they are assignable to the second mobile station, as second codes,

a fourth selecting unit, when there is no second code, for selecting oneor more than one first codes if their lower codes have been assigned tothe first mobile station, as fifth codes,

an assigned code detecting unit for detecting a code lower than thefifth codes and assigned to the first mobile station as a fourth code,

a switchable code detecting unit for detecting a code to whichswitchable from the fourth code, for the first mobile station, as asixth code,

a code switch directing unit for directing the first mobile station toswitch from the fourth code to the sixth code, and

an assigning unit for assigning a fifth code to the second mobilestation after switching all the fourth codes to other codes.

According to another aspect of the present invention,

the code-switching/code-assignment processing unit includes a codeswitch informing unit for informing that the fourth code having beenused by the first mobile station can be switched to a sixth code,

one of the plurality of base stations includes a timing informationsending unit for sending timing information of switching from the fourthcode to the sixth code to the first mobile station,

the first mobile station includes a code switching unit for switchingthe fourth code to the sixth code based on the informing of thecode-switching/code-assignment processing unit and the timinginformation of the one of the base stations,

the one of the plurality of base stations includes a switching unit forswitching downlink transmission codes at time when the timinginformation is sent to the first mobile station, and

the code-switching/code-assignment processing unit includes a codereleasing unit for releasing the fourth code used by the first mobilestation, at the time when the timing information is sent to the firstmobile station.

According to another aspect of the present invention, thecode-switching/code-assignment processing unit includes a first codeswitching unit for informing the first mobile station that a fourth codebeing used by the first mobile station is to be switched to a sixthcode,

one of the plurality of base stations includes a transmitting unit forperforming transmission using both the fourth code and the sixth code tothe first mobile station,

the first mobile station includes a regenerating unit for receiving boththe fourth code and the sixth code and generating reception informationby performing maximum ratio combination, a second code switching unitfor switching a state of synthesizing maximum ratio to a state ofreceiving only the sixth code based on own timing, and a switchingcomplete informing unit for informing that code switching has beencompleted in the first mobile station, and

the code-switching/code-assignment processing unit includes a codereleasing unit for releasing the fourth code used by the first mobilestation, based on the informing from the first mobile station.

According to another aspect of the code assigning apparatus of thepresent invention, the code selecting unit is provided in either one ofthe plurality of base stations or the base station controlling unit.

According to another aspect of the code assigning apparatus of thepresent invention, the code-switching/code-assignment processing unit isprovided in either one of the plurality of base stations or the basestation controlling unit.

According to one aspect of a method of assigning codes of the presentinvention, used in a radio communication system including a base stationcontrolling apparatus, a plurality of base stations, and a plurality ofmobile stations, employing CDMA (Code Division Multiple Access) whichuses codes of tree structured orthogonal multi-spreading factorsequences as spreading codes, for radio access between the plurality ofbase stations and the plurality of mobile stations, and providingmulti-rate transmission between the plurality of mobile stations and theplurality of base stations, the method of assigning codes comprises thesteps of

selecting one or more than one codes corresponding to rate informationincluded in a message from one of the plurality of mobile stations, asfirst codes,

selecting one or more than one first codes if they are assignable to theone of the plurality of mobile stations, as second codes,

retrieving codes upper than the second codes one by one,

detecting not-assignable codes, which are assigned to another of theplurality of mobile stations, out of the codes upper than the secondcodes, as third codes,

detecting each level of the third codes,

selecting one of the second codes whose upper third code is in a lowestlevel in the tree structure, and

assigning the one of the second codes selected by the above step to oneof the plurality of mobile stations.

According to another aspect of the method of assigning codes of thepresent invention comprises the steps of

selecting one or more than one codes corresponding to rate informationincluded in a message from the second mobile station as first codes,

selecting one or more than one first codes if they are assignable to thesecond mobile station as second codes,

when there is no second code, selecting one or more than one first codesif their lower codes have been assigned to the first mobile station, asfifth codes,

detecting a code lower than the fifth codes and assigned to the firstmobile station, as a fourth code,

detecting a code to which switchable from the fourth code for the firstmobile station, as a sixth code,

directing the first mobile station to switch from the fourth code to thesixth code, and

assigning a fifth code to the second mobile station after switching allthe fourth codes to other codes.

According to another aspect of the method of assigning codes of thepresent invention comprises the steps of

informing that a fourth code having been used by the first mobilestation can be switched to a sixth code,

sending timing information of switching from the fourth code to thesixth code to the first mobile station,

switching the fourth code to the sixth code based on the informing ofthe informing step and the timing information of the sending timinginformation step,

switching downlink transmission codes based on the timing informationsent to the first mobile station, and

releasing the fourth code used by the first mobile station, based on thetiming information.

According to another aspect of the method of assigning codes of thepresent invention comprises the steps of

informing the first mobile station that a fourth code being used by thefirst mobile station is to be switched to a sixth code,

performing downlink transmission using both the fourth code and thesixth code to the first mobile station,

receiving both the fourth code and the sixth code,

generating reception information by performing maximum ratiocombination,

switching a state of synthesizing maximum ratio to a state of receivingonly the sixth code based on own timing,

informing that code switching has been completed in the first mobilestation, and

releasing the fourth code used by the first mobile station, based on theinforming from the first mobile station.

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawing wherein one example isillustrated by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a configuration of radio communication system applying acode assignment method according to the present invention;

FIG. 2 illustrates sequence of a code assignment procedure according tothe present invention;

FIG. 3 shows a code structure used for the code assignment procedure ofFIG. 2;

FIG. 4 is a flowchart showing a process of the code assignment procedureof FIG. 2;

FIG. 5 illustrates sequence of another code assignment procedureaccording to the present invention;

FIG. 6 shows a code structure used for a code switching procedure ofFIG. 5;

FIG. 7 shows a code structure used for selecting a code-switchingcandidate code;

FIG. 8 is a flowchart showing a process of the code assignment procedureof FIG. 5;

FIG. 9 illustrates sequence of another code assignment procedureaccording to the present invention;

FIG. 10 illustrates sequence of another code switching procedureaccording to the present invention;

FIG. 11 shows a tree structure of codes having tree structuredorthogonal multi-spreading factor sequence, used in a conventional art;

FIG. 12 shows a configuration of a code selecting unit in a base stationcontroller according to the present invention;

FIG. 13 shows a level list according to the present invention;

FIG. 14 shows configurations of a code selecting unit and acode-switching/code-assignment processing unit, in a base stationcontroller according to the present invention;

FIG. 15 shows a switching list according to the present invention;

FIG. 16 shows a system structure according to the present invention; and

FIG. 17 shows a system structure according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 1 shows a configuration of radio communication system applying acode assignment method according to the present embodiment. FIG. 2illustrates sequence of a code assignment procedure according to thepresent embodiment. FIG. 3 shows a code structure example of the codeassignment procedure of FIG. 2. FIG. 4 is a flowchart showing a processof the code assignment procedure of FIG. 2. FIG. 12 shows aconfiguration of a base station controller 1. Referring to FIGS. 1, 2,3, 4, and 12, one embodiment of code assignment performed in a basestation 2 and the base station controller 1 according to the presentinvention will be described.

FIG. 1, showing a configuration of radio communication system of thepresent embodiment and other embodiments, is composed of plural mobilestations 3 a, 3 b and 3 c, plural base stations 2 a, and 2 b, and thebase station controller 1 which controls the plural base stations 2 aand 2 b. The mobile stations 3 a, 3 b and 3 c are just called as a“mobile station 3” in the case of describing each mobile station beingunnecessary. The base stations 2 a and 2 b are also called as a “basestation 2” in the case of describing each base station beingunnecessary. The mobile station 3 is connected to the base station 2 viaa radio channel. The radio channel utilizes the Code Division MultipleAccess (CDMA) system as a radio access system, and uses spreading codeshaving tree structured orthogonal multi-spreading factor sequences.According to the radio communication system of the present embodiment,it is possible to set up multiple rates. Namely, the base station 2 andthe mobile station 3 can set up channels of plural-kinds rates for eachcall, using the radio channel. As orthogonal multi spreading codes areused, a channel having a double transmission rate can be set up inproportion as a code level goes up one by one.

FIG. 2 illustrates sequence of a code assignment procedure in responsiveto a call from the mobile station 3. Referring to FIGS. 1 and 2, thecode assignment procedure regarding the base station controller 1, thebase station 2 and the mobile station 3 will now be explained. First, aradio channel set-up request message is transmitted from the mobilestation 3 to the base station controller 1 via the base station 2. Thebase station controller 1 analyzes the message in order to detect atransmission rate requested by the mobile station 3. The base stationcontroller 1 determines a pair of codes for transmission to be used bythe mobile station 3 and the base station 2, based on the codeassignment process stated later. Then, the base station controller Itransmits the radio channel set-up request message to the base station2.

The radio channel set-up request message includes information of thecode pair. Receiving the message, the base station 2 begins to preparefor reception/transmission based on an appointed code, and transmits aradio channel set-up complete message to the base station controller 1.On receiving the radio channel set-up complete message, the base stationcontroller 1 transmits the radio channel set-up complete messageappointing the pair of codes to the mobile station 3. After receivingthe message, the mobile station 3 starts communication with the basestation 2, based on the appointed code.

As stated above, the communication channel between the mobile station 3and the base station 2 is set up based on the request from the mobilestation 3. A code selection process, performed in the base stationcontroller 1 for the mobile station 3 and the base station 2 isexplained with reference to FIGS. 3, 4 and 12. FIG. 3 shows a treestructure of codes having orthogonal multi-spreading factor sequence. InFIG. 3, the tree structure is composed of four levels; level 1 at thetop through level 4 at the bottom, defined just for convenience. Asthere are four levels in this case, the channel transmission rate usingthe top level (level 1) code is eight times as fast as that of channelusing the lowest level (level 4) code. The channel transmission rateusing level 2 code is four times the rate of channel using level 4 code.The channel transmission rate using level 3 code is twice the rate ofchannel using level 4 code.

Cx(y) in FIG. 3 represents a kind of codes; x stands for a code level, ystands for an identification number in the same code level, and ◯ standsfor a code. In the tree structured orthogonal multi spreading sequencecodes, codes lower than a specific code being used (that is, largernumber level codes connected with the specific code by branches in FIG.3) can not be used because of keeping the orthogonality characteristic.

In addition, codes upper than the specific code being used (that is,smaller number level codes connected with the specific code through onlyupward branches) also can not be utilized. When C₃(2) is being used inFIG. 3, C₁(1), C₂(1), C₄(3) and C₄(4) can not be used. Therefore, it isnecessary to appropriately assign a code to a new call from the mobilestation 3.

FIG. 12 shows a configuration of a code selecting unit 10 in the basestation controller 1. FIG. 4 is a flowchart showing code assignmentprocesses, for the mobile station 3 and the base station 2, performed inthe code selecting unit 10. When a first selector 11 of the base stationcontroller 1 receives the radio channel set-up request message from themobile station 3 (S0101), the first selector 11 analyses rateinformation in the message (S0102), and determines a code level neededfor the mobile station 3 and the base station 2 (S0103). In FIG. 3, forinstance, the code level requested by the mobile station 3 is level 3.Secondly, a second selector 12 of the base station controller 1 selectscandidate codes which can be used in the determined level (S0104). InFIG. 3, C₃(1), C₃(3) and C₃(4) are selected as the candidate codes.

A level detector 13 of the base controller 1 selects a code out of thecandidate codes (S0105), selects another code in a level one more upperthan the selected code (S0106), and judges whether or not the one moreupper level code can be assigned (S0107). In FIG. 3, if the candidatecode is C₃(1), the one more upper level code is C₂(1). Then, when theone more upper level code is able to be assigned, the judging procedureis repeated upwards along the branches until it comes to a code whichcan not be assigned (S1018, S0109). If a code that is not assignable isdetected, the code and its level are memorized in a level list 16 foreach of the candidate codes (S0107, S0110). When C₃(1) in FIG. 3 is thecandidate code, one more upper code C₂(1) is not assignable. Then,C₃(1), C₂(1) and the level 2 are stored in the level list 16 as shown inFIG. 13. This procedure is performed for each candidate code to completethe level list 16 shown in FIG. 13 (S0111).

A third selector 14 selects a candidate code whose upper not-assignablecode has the lowest level, in the level list 16 (S0112). Then, thecandidate code is selected to be assigned to the mobile station 3(S0113). If there are several candidate codes whose upper not-assignablecodes have the same code level, any of the candidate codes can beselected. If a candidate code has no upper not-assignable code, the toplevel code is regarded as the upper not-assignable code. As shown inFIG. 13, C₂(1) being the upper not-assignable code and level 2 areselected for the candidate code C₃(1) in FIG. 3. C₁(1) and level 1 arefor the candidate code C₃(3), and C₁(1) and level 1 are for thecandidate code C₃(4). Therefore, C₃(1), whose upper not-assignable codeis C₂(1), is selected as a code to be assigned. According to thisassigning method, C₃(3) and C₃(4) in FIG. 3 are not selected. The codeC₃(1) is assigned to the mobile station 3 by a code assigning unit 15.If a new call corresponding to level 2 is requested after the callcorresponding to level 3 has been in use as shown in FIG. 3, C₂(2) canbe assigned to the new call.

According to the present assigning method, a channel mismatch at thecode assigning time of a new call starting, caused by the tree structurecharacteristic, is avoided. Therefore, a code assignment for multi-ratetransmission can be performed without deteriorating the channelutilization efficiency. It is also acceptable to provide the codeselecting unit 10 of FIG. 12 in the base station 2 instead of the basestation controller 1.

Embodiment 2

FIG. 5 illustrates a code assignment sequence showing a code switchingprocedure, according to the present embodiment. FIG. 6 shows a codestructure applied for the code switching procedure of FIG. 5. FIG. 7shows a code structure used in selecting a candidate code for the codeswitching. FIG. 8 is a procedure flowchart for the code assignmentsequence of FIG. 5. FIG. 14 shows a configuration of the base stationcontroller according to the present embodiment. Referring to FIGS. 1, 5,6, 7, 8 and 14, the code assignment according to the present embodimentwill now be described.

The code switching is explained with reference to FIG. 6 showing a codeassignment state change. The same code definition as FIG. 3 is used inFIG. 6. As stated in Embodiment 1, when a code has been already assignedto the mobile station 3, it is impossible to newly assign a code inupper level than the assigned code to another mobile station 3, becauseof the characteristic of spreading codes having tree structuredorthogonal multi-spreading factor. In the left of FIG. 6, as C₄(1) andC₄(3) have been already assigned, it is impossible to assign C₃(1) andC₃(2) to another mobile station 3. Accordingly, if there is a callrequesting a transmission rate corresponding to level 3 at this time,the call is to be lost. By switching the code from C₄(3) to C₄(2),however, C₃(2) can be assigned, so that the call requesting thetransmission rate corresponding to level 3 is accepted.

Referring to FIGS. 1 and 5, the code assignment procedure and the codeswitching procedure regarding the base station controller 1, the basestation 2, and the mobile station 3 will now be explained. In FIG. 1, amobile station #1 (3 a) has been already used, and a mobile station #2(3 b) newly makes a call. As shown in FIG. 5, the mobile station #2 (3b) transmits a radio channel set-up request message indicating atransmission rate, to the base station controller 1 as stated inEmbodiment 1.

When there is no assignable code as shown in the left of FIG. 6, it isnecessary to perform code switching. Therefore, the mobile station #1 (3a) and a code are selected for the code switching, based on a methodstated later. The radio channel set-up request message is transmitted toa base station 2 a in order to assign the selected code to the mobilestation #2 (3 b).

The base station 2 a judges whether the code appointed in the radiochannel set-up request message can be used or not. In this case, as thecode is being used by the mobile station #1 (3 a), it is judged to benot usable. Then, a code switching request is transmitted to the basestation controller 1. On receiving the code switching request from thebase station 2 a, the base station controller 1 transmits a codeswitching request message including information of code after switchingto the mobile station #1 (3 a). In the case of FIG. 6, the base stationcontroller 1 defines C₄(2) as the code after-switching in the codeswitching request message.

When the mobile station #1 (3 a) receives the code switching requestmessage, the mobile station #1 (3 a) switches the original E code to thetarget code (code after switching) (C₄(2) in FIG. 6), and transmits acode switching complete message to the base station controller 1. Thebase station controller 1 judges, by receiving the code switchingcomplete message, that the code has been switched in the mobile station#1 (3 a). (The state has been changed from the left side to the rightside in FIG. 6.) Then, the base station controller 1 transmits the codeswitching complete message to the base station 2 a. After receiving thecode switching complete message, the base station 2 a transmits a radiochannel set-up complete message to the base station controller 1. Thebase station controller 1 transmits the radio channel set-up completemessage to the mobile station #2 (3 b) in order to assign an assignableand requested-level code whose level is corresponding to thetransmission rate requested by the mobile station #2 (3 b) (that is,C₃(2) in FIG. 6).

By performing the above procedures, a new radio channel requested by themobile station 3 has been set up between the mobile station 3 and thebase station 2. Now, the code switching procedure, for the mobilestation #1 (3 a) and the base station 2 a, performed in the base stationcontroller 1, and the code assigning procedure, for the mobile station#2 (3 b) and the base station 2 a, performed in the controller 1 areexplained with reference to FIGS. 7, 8 and 14. Similar to FIG. 3, FIG. 7shows a tree structure of codes having orthogonal multi-spreading factorsequence. The candidate code/not-assignable in the figure represents anunused code which is corresponding to a requested transmission rate andwhose lower level code has been already assigned. FIG. 14 shows aconfiguration of a code-switching/code-assignment processing unit 20 inthe base station controller 1. FIG. 8 is a flowchart showing a codeswitching and a code assigning process performed in thecode-switching/code-assignment processing unit 20.

Similar to Embodiment 1, when the first selector 11 of the base stationcontroller 1 receives the radio channel set-up request message from themobile station#2 (3 b) (S0101), the first selector 11 analyzes rateinformation in the message (S0102) and determines a code level in thetree structure corresponding to the rate information (S0103). In FIG. 7,for instance, the code level corresponding to the rate information islevel 3. The second selector 12 of the base station controller 1retrieves an assignable code of the determined level (S0104). When thereis no assignable candidate code of the determined level (S0201), afourth selector 21 selects a code which is not assignable and has notbeen itself assigned, as a candidate code (S0204). In FIG. 7, C₃(1) andC₃(2) are such codes. In the case of there being no code which is notassignable and has not been itself assigned yet (S0202:No), the originalcall becomes lost (S0203).

An assigned code detector 22 selects a code out of candidate codes(C₃(2) in FIG. 7) (S0205), and detects an assigned code in lower levelthan the selected candidate code. (In FIG. 7 case, C₄(3)) (S0206). Aswitchable code detector 23 retrieves codes to see whether there is aswitchable code at the same level as the above assigned code or not.(S0208). When there is a switchable code in the same level as theassigned code (C₄(2) in FIG. 7), the candidate code (C₃(2)), theassigned code (C₄(3)) and the switchable code (C₄(2)) are stored in aswitching list 26 as shown in FIG. 15 (S0210). This procedure isperformed for every candidate code and every assigned code at the lowerlevel than the candidate code. (S0207, S0209, S0211). In the case ofthere being candidate codes, the switchable code detector 23 selects onecandidate code having the least number of assigned codes at its lowerlevel, as an assignment target code (S0213).

In the above case, all the assigned codes have their switchable codes inthe same level. In FIG. 7, there are two candidate codes: C₃(1) andC₃(2). As shown in FIG. 15, either of C₃(1) and C₃(2) has one assignedcode (C₄(1) is for C₃(1), and C₄(3 s) is for C₃(2)), and both thecandidate codes C₃(1) and C₃(2) have their switchable codes (C₄(4) forC₃(1) and C₄(2) for C₃(2)) in the same level (level 4). Therefore,either of C₃(1) and C₃(2) can be selected as the assignment target code.

A code switch directing unit 24 switches the assigned code at the lowerlevel of the selected assignment target code to the stored switchablecode (S0214). In the case of selecting C₃(2) as the assignment targetcode in FIG. 7, C₄(3) is switched to C₄(2). The code used by the mobilestation #1 (3 a) in FIG. 5 is corresponding to the assigned code. Anassigning unit 25 assigns the selected assignment target code to themobile station #2 (3 b) (S0215).

The switching possibility is checked for all the assigned codes at thelower level of all the candidate codes, in the present embodiment. Thechecking process, however, can be completed at the first time ofdetecting a candidate code which has an assigned code to be switched atthe lower level.

Even when a channel mismatch exists, according to the presentembodiment, the call loss rate is reduced because a new high rate callcan be achieved by switching a code being used in the mismatch channel.It is also acceptable to provide the code selecting unit 10 and thecode-switching/code-assignment processing unit 20 of FIG. 14 in the basestation 2 instead of the base station controller 1.

Embodiment 3

FIG. 9 illustrates a code assignment sequence showing a code switchingprocedure, according to the present embodiment. FIG. 16 shows a systemstructure. Referring to FIGS. 1, 9, and 16, the code switching accordingto the present embodiment will be explained below.

As stated in Embodiment 2, it is sometimes necessary to switch codesduring the communication. The code switching during the communicationshould be simultaneously performed at the base station 2 and the mobilestation 3 in order not to stop the communication and so as to reduceinterfering in other communication. The simultaneous switching isperformed based on code switch timing information sent from a timinginformation sending unit 33 in the base station 2 to the mobile station3. FIG. 9 illustrates procedures of sending the code switch timinginformation from the base station 2 to the mobile station 3.

The procedures, from transmitting a radio channel set-up request messageby the mobile station #2 (3 b) up to transmitting a code switchingrequest message to the mobile station #1 (3 a) by the base stationcontroller 1, are the same as Embodiment 2 shown in FIG. 5. Therefore,procedures after the above will now be described in the presentembodiment. A code switch informing unit 31 of the base stationcontroller 1 transmits a code switching request message indicating atarget code (code after switching) to the mobile station #1 (3 a). Onreceiving the code switching request message, a code switching unit 35of the mobile station #1 (3 a) starts preparing for the code switchingand transmits a code switching response message to the code switchinforming unit 31 of the base station controller 1.

After receiving the code switching response message, the code switchinforming unit 31 transmits the message indicating that the code of themobile station #1 (3 a) can be switched, to the base station 2 a.Receiving the code switching response message, the timing informationsending unit 33 of the base station 2 a transmits a code switching startmessage to the mobile station #1 (3 a). This code switching startmessage includes start timing information for the code switching. Then,if the radio channel is composed of frames, the code switching startmessage can be time information per frame.

It is acceptable to switch at the time of frame N (N is equal to 1 or aninteger more than 1) after receiving the code switching start message.It is also acceptable for the timing information to use a code period ofthe spreading code. Thus, a switching unit 34 is synchronized with thecode switching unit 35 in order to switch the code.

Receiving the code switching start message, the code switching unit 35of the mobile station #1 (3 a) switches the original code (code beforeswitching) to the target code (code after switching) based on the timeprescription specified in advance, using the timing information in themessage. Then, the code switching unit 35 transmits a code switchingcomplete message to the timing information sending unit 33 in the basestation 2 a using the target code. By receiving the code switchingcomplete message, the timing information sending unit 33 judges that thecode switching has been properly completed, and transmits the codeswitching complete message to the base station controller 1. Byreceiving the code switching complete message, a code releasing unit 32of the base station controller 1 judges that the code used by the mobilestation #1 (3 a) has been released, and transmits a radio channel set-upcomplete message for assigning the code used by the mobile station #1 (3a) to the mobile station #2 (3 b).

As the code switch timing between the mobile station 3 and the basestation 2 can be set up according to the present embodiment, it is notnecessary for the base station 2 to simultaneously perform reception andtransmission using both the original code and the target code.Consequently, interfering with other communications is reduced.

Embodiment 4

FIG. 10 illustrates a code assignment sequence showing a code switchingprocedure using the maximum ratio combination of the mobile station 3,according to the present embodiment. FIG. 17 shows a system structure.Referring to FIGS. 10 and 17, the code switching according to thepresent embodiment will now be described.

The procedures, from transmitting the radio channel set-up requestmessage by the mobile station #2 (3 b) up to transmitting the codeswitching request message by the base station 2 a to the base stationcontroller 1, are the same as Embodiment 2 shown in FIG. 5. Therefore,procedures after the above will now be described in the presentembodiment.

As shown in FIG. 10, after the base station 2 a sends the code switchingrequest message to the base station controller 1, a transmitting unit 43of the base station 2 a performs reception and transmission with aregenerating unit 44 of the mobile station #1 (3 a) using both theoriginal code (code before switching) and the target code (code afterswitching). When the base station controller 1 receives the codeswitching request message from the base station 2 a, a first codeswitching unit 41 of the base station controller 1 transmits the messageto the mobile station #1 (3 a), and instructs the regenerating unit 44of the mobile station #1 (3 a) to switch the code. On receiving the codeswitching request message, the regenerating unit 44 begins to receivesignals based on the maximum ratio combination, using both the originalcode (code just in use) and the target code appointed by the codeswitching request message.

Regarding the transmission, either of the following methods isacceptable. One is to independently switch the code by using a secondcode switching unit 45 of the mobile station #1 (3 a). The other is totransmit signals from the mobile station #1 (3 a) with using both theoriginal code in use and the target code. In this case of transmittingwith using both the codes, it is also acceptable to perform the maximumratio combination at the base station 2.

When the second code switching unit 45 of the mobile station #1 (3 a),in which the reception has been performed by the regenerating unit 44based on the maximum ratio combination, begins to independently receivesignals using the target code only, a switching complete informing unit46 of the mobile station #1 (3 a) transmits a code switching completemessage to a code releasing unit 42 of the base station controller 1with using the target code. Then, the code releasing unit 42 judges thatthe code having been used in the mobile station #1 (3 a) until this timeis released and the code switching is completed. The code releasing unit42 transmits the code switching complete message to the base station 2a. On receiving the code switching complete message from the basestation controller 1, the base station 2 a stops transmitting signals tothe mobile station #1 (3 a) using the original code, releases theoriginal code, prepares for the reception and the transmission with themobile station #2 (3 b) using the original code, and transmits a radiochannel set-up complete message to the base station controller 1.

After receiving the radio channel set-up complete message from the basestation 2 a, the base station controller 1 transmits the messageindicating to set up the original code, having been used in the mobilestation #1 (3 a), for the mobile station #2 (3 b). As stated above, thecode switching process using the maximum ratio combination has beenperformed.

According to the present embodiment procedures, the code switch timingcan be achieved based on own timing of the mobile station 3 withoutdeteriorating the channel quality. Namely, the time needed for codeswitching can be reduced.

In addition, it is also acceptable that the code assignment iscontrolled by the base station 2 instead of the base station controller1.

Having thus described several particular embodiments of the invention,various alterations, modifications, and improvements will readily occurto those skilled in the art. Such alterations, modifications, andimprovements are intended to be part of this disclosure, and areintended to be within the spirit and scope of the invention.Accordingly, the foregoing description is by way of example only, andnot intended to be limiting. The invention is limited only as defined inthe following claims and the equivalents thereto.

1. A radio communication method used for a radio communication system employing CDMA (Code Division Multiple Access) for radio access and providing multi-rate transmission, the radio communication system comprising: a first station including one or more mobile stations; and a second station including one or more base stations communicating with at least one of the plurality of mobile stations of the first station and a base station controlling apparatus controlling the one or more base stations, and the radio communication method comprising: transmitting a second code to one of the plurality of mobile stations of the first station, wherein a first code, being used by the one of the plurality of mobile stations of the first station, is to be switched to a second code during a communication; transmitting timing information regarding timing of switching the first code to the second code to the one of the plurality of mobile stations of the first station; switching, by the one of the plurality of mobile stations of the first station, the first code to the second code based on the timing information; switching, by one of the plurality of the base stations of the second station, the first code to the second code in synchronization with switching the first code to the second code by the one of the plurality of mobile stations of the first station; transmitting, by the one of the plurality of mobile stations of the first station, a code switching complete information from the one of the plurality of mobile stations of the first station; and releasing, by the second station, the first code in response to a code switching complete information from the one of the plurality of mobile stations of the first station.
 2. A radio communication system employing CDMA (Code Division Multiple Access) for radio access and providing multi-rate transmission, comprising: a first station including one or more mobile stations; a second station including one or more base stations communicating with at least one of the plurality of mobile stations of the first station and a base station controlling apparatus controlling the one or more base stations; a code information transmitting unit configured to transmit a second code to one of the plurality of mobile stations of the first station, wherein a first code, being used by the one of the plurality of mobile stations of the first station, is to be switched to a second code during a communication; a timing information transmitting unit configured to transmit timing information regarding timing of switching the first code to the second code to the one of the plurality of mobile stations of the first station; a code switching unit located at the one of the plurality of mobile stations of the first station and configured to switch the first code to the second code based on the timing information transmitted by the timing information transmitting unit; a switching unit located at one of the plurality of the base stations of the second station and configured to switch the first code to the second code in synchronization with switching the first code to the second code by the code switching unit at the one of the plurality of mobile stations of the first station; a transmitting unit located at the one of the plurality of mobile stations of the first station, configured to transmit a code switching complete information from the one of the plurality of mobile stations of the first station; and a code releasing unit located in the second station and configured to release the first code in response to a code switching complete information from the one of the plurality of mobile stations of the first station. 